I had the same problem and I've searched for ready made solutions for over an year before I found a guy that reverse-engineers and builds ready-made boards to install in my intercom for less than 30 euro.

I'm unsure if I should post the link or not as it's specific to Romania, but I love how janky the buids are: https://www.olx.ro/d/oferta/automatizare-interfon-electra-cu...

Some years ago I had an older analog intercom and added some intelligence for the open button, ignoring the audio part. Doing it with an ESP01 was trivial and I only needed access to my intercom box inside the apartment. The first issue I ran into was that no matter how much I optimized, the power consumption was high and made the thing semi-useless. Then I got smarter and powered it from the 24V lines coming from the intercom system. That worked great until I realized that where I live this counts as stealing electricity so I scratched that, why take the chance that the building administrator notices something and I get burned.

Eventually I got a Nuki Opener which works with all kinds of intercoms and is way less effort. Janky builds are awesome but better for the playground than as a solution you really want to be reliable for the whole family.

P.S. The code from the article should be linked more prominently [0], for anyone who wants to tinker.

[0] https://github.com/ImTheSquid/doorbell2